Typical vane pumps known in the art include, e.g., the one illustrated in FIG. 8. This vane pump 1 has a rotor chamber 2 and a rotor 3 eccentrically accommodated in the rotor chamber 2. A plurality of vane grooves 19 is radially formed in the rotor 3 and vanes 4 are slidably moved in the respective vane grooves 19. Each of the vanes 4 is free to move in a radial direction of the rotor 3. As the rotor 3 is rotatably driven, the leading ends of the respective vanes 4 make sliding contact with the inner peripheral surface 2a of the rotor chamber 2, whereby working compartments 5 surrounded by inner surfaces of the rotor chamber 2, an outer peripheral surface 3a of the rotor 3 and the vanes 4 undergo a volume change and a working fluid drawn into the working compartments 5 from an inlet port 6 is discharged through an outlet port 7. As an example, Japanese Patent Laid-Open Application No. H 62-291488 discloses the same vane pump as the one illustrated in FIG. 8.
In such a vane pump, each of the vanes 4 needs to have a relatively great width W (a dimension in the direction perpendicular to a length or protruding direction P of the vane 4 when viewed in a thrust direction, i.e., axial direction, of the rotor 3) in order to increase the strength thereof and also to make itself less susceptible to a dimensional error of the vanes 4 and the vane grooves 19 to thereby assure stable movement of the vanes 4 in a radial direction of the rotor 3.
The width W of each of the vanes 4 needs to be uniform not to vary depending on the locations in the length direction thereof for stable movement in the vane groove 19. For this reason, if the width of the vanes 4 is increased as noted above, it becomes difficult for the leading ends of the vanes 4 to make close sliding contact with the inner peripheral surface 2a of the rotor chamber 2 having a circular cross section. Thus, the working fluid is apt to be leaked through the gaps between the inner peripheral surface 2a of the rotor chamber 2 and the leading ends of the vanes 4. Consequently, pump efficiency is deteriorated.